As a method for forming a plating film on the surface of a steel plate, a method of immersing the steel plate in a pot containing molten aluminum is known. The pot is provided with rolls in a molten metal bath (for example, a sink roll, a support roll) in order to perform continuous plating of a steel plate. A protective layer having resistance to molten metal reaction and resistance to corrosion and abrasion is formed on the surface of the roll.
Patent Literature 1 discloses a powder composition having resistance to molten metal reaction, characterized in that an undercoat layer is formed on the surface of a roll in a molten metal bath and a specific layer is formed on the undercoat layer, where the specific layer is composed of ZrO2.x (x is an oxide selected from the group consisting of CaO, Y2O3, MgO, CeO2, and HfO2) and ZrSiO4 and/or its decomposition product (ZrO2 and SiO2) of which attachment state has been confirmed by X-ray phase analysis. Patent Literature 1 further discloses an undercoat layer composed of one or more ceramic components among metal carbides (WC, TiC, Cr3C2, NbC, ZrC, TaC, MoC, and VC), metal borides (CrB2, TiB2, ZrB2, and MoB2), and metal nitrides (MoN and TiN), and one or more of Co, Ni, Cr, Mo, and W.
Patent Literature 2 discloses that an aqueous solution or slurry of any one or more selected from oxides, borides, and nitrides is applied to the surface of an oxide-based ceramic thermal spray coating film and the inside of pores in the coating film to perform a pore-sealing treatment. Furthermore, in paragraph 0026 of the specification of Patent Literature 2, there is disclosed a pore-sealing technique in which an oxide such as TiO2, ZrO2, SiO2, or MgO, or a nitride such as BN is added to an aqueous solution of chromic anhydride, ammonium chromate, or ammonium dichromate, and the resultant solution is applied to a thermal spray coating film and is heated and fired.